The antioxidants vitamin E (VE) and soy isoflavones (ISF) have potential as important chemoprevention agents for prostate cancer (PCa) as single agents and in combination with commonly used therapeutic agents. Recent improvements in external beam radiotherapy and interstitial brachytherapy (implantation of radioactive pellets) have made this minimally invasive treatment popular among prostate cancer patients. However, dosage-related radio-toxicity usually limits the effective doses that can be used for therapy. Our studies with human PCa cell lines have found additive growth inhibitory effects characterized by cell cycle arrest in androgen-responsive as well as androgen-independent cell lines. Our recent studies have found that treatment with low, physiologically relevant concentrations of ISF and VE decreases the clonogenic survival of PCa cells following irradiation (IR) exposure, evidence of a radiosensitizing effect. This proposed pilot study will further investigate the effects of VE and ISF supplements on the cytotoxicity of clinical anti-neoplastic radiotherapy treatments. The hypothesis is that the treatment of human prostate cancer cells with low concentrations of ISF and VE increases sensitivity to irradiation treatments inhibits growth of cells that survive post-IR, and can reduce the induction of pro-inflammatory cytokines. Specific Aim 1 will be to determine if dietary ISFs and VE, alone or in combination, enhance the cytotoxicity of IR in vivo in PC-3 xenograft tumors in mice. The response of tumors to IR will be characterized for expression of cell cycle and apoptotic pathways, as well as the production of inflammatory cytokines and physiologically relevant blood levels of antioxidants. Specific Aim 2 will determine whether dietary ISF and/or VE exert a specific post-irradiation effect to inhibit progression of recurrent prostate xenograft tumors. This is a targeted neoadjuvant approach to directly assess the potential usefulness of ISF and VE nutritional supplements for long-term benefit post-IR to slow progression of tumor growth. Specific Aim 3 will use a cell culture model to establish genetic and proteomic profiles that are associated with antioxidant-induced radiosensitivity and resistance. Experiments will determine if PC-3 cells overexpressing Bcl- 2, an anti-apoptotic gene, are sensitive to the growth-inhibitory and radiosensitizing effects of ISF and/or VE antioxidants. If a genetic/proteomic signature suggests that it is likely to be radiosensitive tumor, antioxidants and radiation become a more desirable treatment option. This information will serve to identify proteins that may be critical to the tumor microenvironment and tumor invasive phenotype. In summary, the proposed research will provide mechanistic evidence as to whether these nutritional factors enhance, or potentially interfere with concurrent exposure to established cytotoxic therapeutic agents in PCa. Promising results would justify rapid transition to clinical trials, given the popularity of brachytherapy and the increasing consumption of dietary supplements. [unreadable] [unreadable] [unreadable]